1. Field of the Invention
The present invention relates to communications apparatus and methods, particularly but not exclusively for wireless communications, particularly but not exclusively via satellite.
2. Background Art
A number of wireless communications systems have already been proposed to support shared access by many simultaneous communications sessions of different types. For example, the patent publication WO 98/25358 discloses a mobile satellite communications system which supports the variable bandwidth requirements of multiple simultaneous communications sessions.
With this type of system, it is difficult to allocate bandwidth to meet the varying requirements of multiple terminals or sessions, while using the overall bandwidth efficiently. The bandwidth allocation protocols themselves incur a significant signalling overhead, but the more information that is exchanged in these protocols, the better the network is able to adapt to constantly changing demands for bandwidth. Some bandwidth may be designated as being available for contention-based access, which allows data and signalling to be transmitted by mobiles without a bandwidth allocation specific to that mobile, but contention-based access is very bandwidth-inefficient; if the probability of collision is to be kept low, much more bandwidth needs to be allocated than is likely to be actually used.
According to one aspect of the present invention, there is provided a bandwidth allocation protocol in a mobile communications network in which mobiles report their bandwidth requirements to the network, while the network controls the amount of bandwidth that is used by the mobiles in reporting their bandwidth requirements. In this way, the network can control the signalling overhead used by the bandwidth allocation protocol, so as to make more bandwidth available for user data when a channel becomes congested. Alternatively, when the channel is not congested, the network can allow the mobiles to report changes in their bandwidth requirements more quickly, increasing the likelihood that the quality of service demands by active communications sessions on the mobiles can be met.
According to another aspect of the present invention, there is provided a bandwidth allocation protocol in which mobiles indicate both the quantity of data awaiting transmission and the maximum delay requirements for transmission of that data. Instead of indicating individually the delay requirements of each block of data awaiting transmission, the mobiles indicate the total quantity of data awaiting transmission, the maximum delay time of the most urgent portion of said data and the maximum delay time of the least urgent portion. This provides enough information for the network to allocate the necessary bandwidth at the right time to meet the delay requirements of all of the data, while reducing the amount of information needed to indicate the delay requirements.
According to another aspect of the present invention, there is provided a contention-based access protocol for wireless mobile terminals, in which, if a collision occurs between transmission by two mobiles, the mobiles wait for an interval controlled by the network before attempting another contention-based access transmission. In one example, the network transmits an interval range signal to the mobiles, indicating a range for the interval for which the mobiles must wait before retransmitting, and the mobiles select an interval within the range; preferably, this selection is random or pseudo-random. This protocol allows the network to control the likelihood of collision in contention-based access, without necessarily having to allocate more bandwidth to contention-based access; instead, some of the mobiles may be forced to wait longer before retrying.
A further refinement of this protocol involves the network specifying a further increment by which the mobiles must increase the range of the interval each time a subsequent attempt at transmitting the same burst fails. If there are repeated collisions, this indicates that there is not enough contention-based capacity to meet the current demands of the mobiles. According to this refinement, mobiles experiencing repeated collisions are automatically spread over an increasingly broader range of contention-based access capacity to increase the chance of the burst getting through, while the interval range applied by mobiles waiting after their first unsuccessful transmission is not affected.
According to another aspect of the present invention, there is provided a method of managing contention-based access capacity for mobile terminals in a wireless network, in which the network periodically varies the contention-based access capacity available according to the observed usage level and/or collision rate in the previously allocated contention-based access capacity. This adaptive allocation has the advantage of allowing excess allocation of contention-based access capacity to be avoided, while keeping collision rates at an acceptable level.
According to another aspect of the present invention, there is provided a method of allocating return bandwidth to mobiles in a network, in which the network analyses the forward traffic to individual mobiles and predicts the return bandwidth requirements which are likely to result from the forward traffic. At least two possible analytical approaches may be taken, separately or in combination: interpreting the forward traffic by identifying for example requests to send data or to set up specific types of call, and forming a statistical model relating patterns of forward traffic to patterns of return traffic. This aspect has the advantage that the mobile does not need to request additional bandwidth because the network can detect that it is required and allocate it in advance, thus reducing the signalling overhead and reducing the delay before the required bandwidth becomes available.
According to another aspect of the present invention, there is provided a frequency channel allocation scheme in which a wireless network stores associations between forward and return frequency channels, so that when a mobile receiving a forward frequency channel requests return capacity, the network preferentially assigns return bandwidth to the mobile in one or more of the associated return channels. As a result, mobiles assigned capacity in a particular set of return channels are likely to be tuned to a small number of different forward channels, so that bandwidth allocation schedules for return channels need only be transmitted on a small number of associated forward channels.
Aspects of the present invention extend to apparatus adapted to carry out the above methods and protocols, as well as signals generated by these methods and protocols.